1. Field of the Invention
This invention relates to fluid filters, and more particularly to fuel-water separators.
2. Description of the Related Art
Various types of fluid filters currently exist in the art, including filters that have the capability of separating water and/or other contaminants from diesel or other engine fuel before its use in the engine. The basic operation of such filters is to force the fluid through a filter medium or element, with any undesired contaminants remaining on the surface of the filter element. Complications arise with the buildup of contaminants on the filter element surface, clogging or blocking the flow of fluid, necessitating periodic replacement of the element. In the case of spin-on filters, this is generally done by replacing the entire filter apparatus. In the case of top-loading filters, this is generally done by removing the lid or top of the outer housing, replacing the filter element inside, and replacing the top.
Fuel filters that separate out water from the fuel, usually top loading-type filters, generally have an accretion of water on the filter element surface. The water is typically removed from the filter surface by the force of gravity: When enough water accumulates in the same region of the filter element, it coalesces, forming droplets or beads that are large enough and heavy enough to drop into a sump beneath the filter element.
A problem with fuel-water separators is that the longer the filter element is in contact with water that has not yet coalesced sufficiently to drop into the sump, the less hydrophobic the element becomes. Thus the water begins to wick through it and work its way downstream, compromising the performance of the filter. It is therefore advantageous to remove the water from the element as quickly as possible.
Other things being equal, filter element size typically varies with the rate of fuel flow needing to be filtered. More fuel flow requires a larger filter element in order to maintain the same level of performance. Light-duty automotive applications might require a 1.5-liter-per-minute (lpm) flow rate, with a correspondingly small filter element, with heavy-duty, high-horsepower applications having flow rates of 15 lpm or higher, with a correspondingly large filter element. If the filter element is appropriately sized for the fuel flow rate, the fuel-water separator will remove enough water from the fuel to meet the design requirements of the separator.
Even though flow rates are becoming higher in some systems, however, space restrictions or other considerations sometimes make the employment of a larger fuel-water separator impractical. Thus the fuel filter package size cannot always be increased proportionately with the increased flow rate, translating to a drop in filter performance.